Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.95   10.177%   $241.2325   $241.23   $241.25   $241.20  
  Purchase #2 $77.61   10.712%   $85.9236   $85.92   $85.90   $85.90  
  Purchase #3 $123.63   8.114%   $133.6613   $133.66   $133.65   $133.70  
  Purchase #4 $230.91   13.332%   $261.6949   $261.69   $261.70   $261.70  
  Purchase #5 $175.91   13.645%   $199.9129   $199.91   $199.90   $199.90  
  Purchase #6 $25.76   4.262%   $26.8579   $26.86   $26.85   $26.90  
  Purchase #7 $94.30   12.365%   $105.9602   $105.96   $105.95   $106.00  
  7 purchase totals = $947.07       $1,055.2433   $1,055.23   $1,055.20   $1,055.30